Method of producing a semiconductor device with an aluminum or aluminum alloy rear electrode

ABSTRACT

A method of producing a semiconductor device having a thickness of 90 μm to 200 μm and with an electrode on the rear surface, which achieves a high proportion of non-defective devices by optimizing the silicon concentration and thickness of the aluminum-silicon electrode. A surface device structure is formed on a first major surface of a silicon substrate. A buffer layer and a collector layer are formed on the second major surface after grinding to reduce the thickness of the substrate. On the collector layer, a collector electrode is formed including a first layer of an aluminum-silicon film having a thickness of 0.3 μm to 1.0 μm and a silicon concentration of 0.5 percent to 2 percent by weight, preferably not more than 1 percent by weight.

CROSS-REFERENCE TO RELATED APPLICATION

This application is based on, and claims priority to, Japanese PatentApplication No. 2005-179720, filed on Jun. 20, 2005, the contents ofwhich are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method of producing a semiconductordevice, in particular, a power semiconductor device that can be appliedto power conversion apparatuses, has a thickness between 90 to 200 μm,and is provided with an electrode on the rear surface of the device.

2. Description of Related Art

An IGBT (insulated gate bipolar transistor), a type of powersemiconductor device, is a one-chip power device that gives a high speedswitching characteristic and voltage-driving ability, which arespecialties of MOSFETs (or insulated gate type field effecttransistors), and a low forward voltage drop characteristic, which is aspecialty of bipolar transistors. Applications of IGBTs have beenexpanded from industrial fields such as general purpose invertors, ACservo systems, uninterruptible power supplies (UPS), and switching powersupplies, to consumer appliances such as microwave ovens, electric ricecookers, and electric flash lights. IGBTs with low forward voltage dropare being developed employing newly devised chip structures andpromoting loss reduction and efficiency improvement of apparatuses usingthe IGBTs.

IGBTs include punch-through type (PT type), non punch-through type (NPTtype), and field stop type (FS type). A common type of structure is an nchannel, vertical double diffusion structure, except in specialapplications. Accordingly, the following description will be based onexamples of n channel IGBTs, although the description is similarlyapplicable to p channel IGBTs.

A PT type IGBT uses an epitaxial substrate that is formed by epitaxiallygrowing an n+ buffer layer and an n− active layer on a p⁺ semiconductorsubstrate. In an example of a device having a withstand voltage of 600V, while a thickness of about 100 μm is enough for an active layer, anoverall thickness including the p⁺ semiconductor substrate needs to be arelatively large value in the range of 200 to 300 μm. Moreover, theepitaxial substrate is costly.

For reducing costs, NPT type or FS type IGBTs using an FZ substrateinstead of the epitaxial substrate have been developed. The FZ substrateis cut from a semiconductor ingot made by a floating zone (FZ) process.These types of IGBTs have a shallow p+ collector layer with low dose(low injection p+ collector) formed in the rear surface region of thedevice.

FIG. 1 is a sectional view showing a structure of an NPT type IGBTproduced using an FZ substrate. As shown in FIG. 1, an n− semiconductorsubstrate composed of an FZ substrate is used for an active layer 1 andboth a p⁺ base region 2 and an n⁺ emitter region 3 are selectivelyformed in the front surface region of the substrate. On the substratesurface, a gate electrode 5 is formed through a gate oxide film 4. Anemitter electrode 6 is in contact with the emitter region 3 and the baseregion 2, and insulated from the gate electrode 5 by the interlayerinsulation film 7.

A p⁺ collector layer 8 and a collector electrode 9 are formed in therear surface region of the substrate. The overall thickness of thesubstrate is significantly thinner in an NPT type than in a PT type.Hole injection rate being controllable, high speed switching is possiblewithout life time control. Use of an FZ substrate in place of anepitaxial substrate achieves a low cost.

FIG. 2 is a sectional view showing a structure of an FS type IGBT. Asshown in FIG. 2, the device structure in the front surface region of thesubstrate is the same as that in the NPT type of FIG. 1. In the rearsurface region of the substrate, an n buffer layer 10 is providedbetween an n− active layer 1 and a p⁺ collector layer 8. An overallthickness of the substrate in the range of 100 μm to 200 μm is acheivedin the FS type by using an FZ substrate.

The active layer 1, being depleted similarly to the case of the PT type,has a thickness of about 100 μm in a device with a withstand voltage of600 V. Life time control is not needed as in the case of the NPT type.In order to further reduce a forward voltage drop, a type of IGBTcombining a trench structure and an FS type structure has been recentlyproposed. The trench structure has a narrow, deep groove formed in thechip surface region and a MOSFET structure beside the groove.

In producing an FS type IGBT using an FZ substrate, a surface devicestructure is first fabricated in the substrate surface region. Afterthat, the rear surface of the substrate is ground to make the substratethinner. Then, two types of ions are injected from the rear surface ofthe substrate with a reduced thickness, to form a buffer layer 10 and acollector layer 8 in the rear surface region of the substrate through anactivation heat treatment. Finally, a collector electrode 9 is formed ofaluminum or another metal on the surface of collector layer 8 byevaporation or sputtering.

There is also a need for IGBTs exhibiting reverse withstand ability(reverse blocking IGBTs), suitable for use in matrix converters. An nchannel reverse blocking IGBT, for example, has a high concentration ptype isolation region formed in the side region of a normal n channelIGBT and connecting to a collector layer. In producing a reverseblocking IGBT using an FZ substrate, an isolation region is first formedby selective diffusion of impurities from the front surface of thesubstrate. After that, similar to the case of the FS type IGBT,sequentially conducted are: fabrication of a surface device structure,grinding the rear surface of the substrate, ion implantation into therear surface region of the substrate, activation heat treatment, andevaporation or sputtering to form a collector electrode.

In an FS type IGBT, the buffer layer is subjected to a high electricfield when a forward bias voltage is applied; in a reverse blockingIGBT, a PN junction at the rear surface side of the device is subjectedto a high electric field when a reverse bias voltage is applied. Becausethe PN junction in these devices is located at a shallow depth of about0.3 μm in the rear surface region, a small flaw in the rear surfaceregion can cause a punch-through phenomenon leading to loss of devicefunction.

Evaporation or sputtering of a metal such as aluminum for the collectorelectrode is apt to generate spikes 11 of the metal protruding to thesilicon substrate at the interface between a collector layer 8 ofsilicon and a collector electrode 9 of a metallic electrode as shown inFIG. 3. If a spike 11 reaches a buffer layer 10 in an FS type IGBT,unfavorable leakage current results. If a spike 11 reaches a PN junctionin a reverse blocking type IGBT, insufficient reverse withstand voltageand unfavorable reverse leakage current result. It is essential for theabove-mentioned thin IGBT having a thin collector layer to be formedwith a metallic electrode on the rear surface of the substrate to avoidgeneration of the spikes 11 in order to reduce the proportion ofdefective devices.

Japanese Patent Unexamined Publication No. 2002-343980 discloses adiscrete variable capacitance diode for use in high frequency circuitsin which spikes of aluminum into a silicon diffusion layer are avoidedby forming an anode electrode using aluminum-silicon with a siliconconcentration of 3% to 5%. Japanese Patent Unexamined Publication No.2002-343980 also discloses that an aluminum-silicon electrode with asilicon concentration in the range of 1 to 2% has been used to avoidaluminum spikes in large scale integrated circuits (LSI) according tothe prior art.

The aluminum-silicon electrode disclosed in Japanese Patent UnexaminedPublication No. 2002-343980, however, is especially suited for discretevariable capacitance diodes or LSIs, but not suited to avoidinggeneration of aluminum spikes in a rear surface electrode of powersemiconductor devices such as IGBTs. In particular, in a powersemiconductor device in which ion implantation has been conducted on arear surface of the substrate made thin by a back grinding process and ashallow impurity diffusion layer has been formed along the rear surfaceof the substrate, the silicon concentration in the aluminum-siliconelectrode must be optimized to avoid generation of aluminum spikes.Further, because the substrate after the back grinding is very thin, athick aluminum-silicon electrode causes warping in the substrate andundesirably generates cracks in the substrate. Therefore, the thicknessof the aluminum-silicon electrode must be optimized, too.

SUMMARY OF THE INVENTION

In light of the above-described problems in the prior art, an object ofthe present invention is to provide a method of producing asemiconductor device having a thickness of 90 to 200 μm, provided withan electrode on the rear surface of the device, and exhibiting a highproportion of non-defectives, by optimizing thickness and siliconconcentration in the rear electrode, which is composed ofaluminum-silicon or the like.

To solve the above problems and achieve the object, the method ofproducing a semiconductor device according to the invention features thefollowing. In the case of producing an FS type IGBT, a surface devicestructure is first formed in the region of a first major surface of asilicon substrate. After working on a second major surface to reduce thesubstrate to a thickness in the range of 50 μm to 200 μm, a buffer layerand a collector layer are formed in the region of the second majorsurface by ion implantation, for example. After that, analuminum-silicon film, which is a rear electrode, is formed in contactwith the collector layer.

The silicon concentration of the aluminum-silicon film is preferably atleast 0.5 percent by weight. The thickness of the aluminum-silicon filmis preferably in the range of 0.3 μm to 1.0 μm. When the thickness ofthe aluminum-silicon film is in this range, the silicon concentration ofthe aluminum-silicon film is preferably at most 2.0 percent by weight,more preferably at most 1 percent by weight. A buffer metal film oftitanium or molybdenum can be formed on the surface of thealuminum-silicon film. A soldering metal film can be formed on thebuffer metal film, and a protective metal film can be formed on thesoldering metal film.

In the case of producing a reverse blocking IGBT, a film of aluminum oran aluminum alloy having a thickness of at least 0.3 μm is formed incontact with the collector layer for a rear electrode. A siliconconcentration in the aluminum alloy film need not be specified. When thealuminum alloy film is thinner than 0.3 μm, say about 0.1 μm, the rearelectrode can be composed of an aluminum alloy film with a siliconconcentration of 2 percent by weight or more in contact with thecollector layer. This measure can be applied to an FS type IGBT. Themethod of the invention prevents generation of aluminum spikes thatcauses leakage current defects, reverse withstand voltage defect, andreverse leakage current defects.

According to a method of producing a semiconductor device of theinvention, the generation of aluminum spikes can be avoided byoptimizing a thickness and silicon concentration of the rear electrode,which is composed of aluminum-silicon or the like. Therefore, the methodof the invention has an effect of producing, with a high proportion ofnon-defective devices, semiconductor devices having a thickness in therange of 90 μm to 200 μm and provided with an electrode on the rearsurface of the device.

DETAILED DESCRIPTION OF THE INVENTION

Now, some preferred embodiments according to a method of producing asemiconductor device will be described in detail with reference to theaccompanying drawings. In the specification and drawings, a layer orregion preceded by the letter n or p means that the majority carriersare electrons or holes, respectively, in the layer or region. The signs“+” or “−” put on the n or p means higher impurity concentration orlower impurity concentration, respectively, than in a layer or regionwithout the sign. In the description of embodiments and accompanyingdrawings, like symbols are given to like components.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view of a structure of an NPT type IGBT.

FIG. 2 is a sectional view of a structure of an FS type IGBT.

FIG. 3 is a sectional view showing spikes protruding from a metalelectrode into a silicon layer.

FIG. 4 is a sectional view of an FS type IGBT to illustrate a productionmethod of the first embodiment.

FIG. 5 is a sectional view of an FS type IGBT to illustrate a productionmethod of the first embodiment.

FIG. 6 is a sectional view of an FS type IGBT to illustrate a productionmethod of first embodiment.

FIG. 7 is a sectional view of an FS type IGBT to illustrate a productionmethod of the first embodiment.

FIG. 8 is a sectional view of an FS type IGBT to illustrate a productionmethod of the first embodiment.

FIG. 9 is an electron micrograph of a silicon surface after removing analuminum-silicon film.

FIG. 10 is an electron micrograph of a silicon surface after removing analuminum film.

FIG. 11 is a sectional view of a reverse blocking type IGBT toillustrate a production method of the second embodiment.

FIG. 12 is a sectional view of a reverse blocking type IGBT toillustrate a production method of the second embodiment.

FIG. 13 is a sectional view of a reverse blocking type IGBT toillustrate a production method of the second embodiment.

FIG. 14 is a sectional view of a reverse blocking type IGBT toillustrate a production method of the second embodiment.

FIG. 15 is an electron micrograph of a silicon surface after removing analuminum film.

FIG. 16 is an electron micrograph of a silicon surface after removing analuminum film.

FIG. 17 is an electron micrograph of a silicon surface after removing analuminum film.

FIG. 18 is an electron micrograph of a silicon surface after removing analuminum film.

FIG. 19 is an electron micrograph of a silicon surface after removing analuminum film.

FIG. 20 shows the depth of flaws due to aluminum spikes and theproportion of non-defective devices in dependence on the thickness ofthe aluminum film.

FIG. 21 is an electron micrograph of a silicon surface after removing analuminum-silicon film.

FIG. 22 is an electron micrograph of a silicon surface after removing analuminum-silicon film.

FIG. 23 is an electron micrograph of a silicon surface after removing analuminum-silicon film.

FIG. 24 shows the proportion of non-defective devices in dependence onthe thickness of the aluminum-silicon film.

FIG. 25 shows the proportion of non-defective devices in dependence onthe silicon concentration of the aluminum-silicon film.

DETAILED DESCRIPTION OF THE DRAWINGS First Embodiment

FIG. 2 and FIG. 4 through 8 are sectional views illustrating a method ofproducing an FS type IGBT according to the invention. Referring to FIG.2 and FIG. 4, in the front surface region of an n− FZ substrate (FZ-N),which Works as an active layer (a drift layer) 1, a front surface regiondevice structure 12 is first formed consisting of a base region, anemitter region, a gate oxide film, a gate electrode, an interlayerinsulation film, an emitter electrode, and an insulation protective film(omitted in FIG. 2).

The gate oxide film may be made of silicon oxide (SiO₂), for example.The gate electrode may be made of polysilicon, for example. Theinterlayer insulation film may be made of BPSG, for example. The emitterelectrode may be made of aluminum-silicon, for example. Thealuminum-silicon film is heat treated at a relatively low temperature inthe range of 350° C. to 450° C. in order to obtain a low resistancewiring with stable joining ability. The insulation protective film maybe made of polyimide, for example.

Then, as shown in FIG. 5, the rear surface of the substrate is ground byone or more methods that may be selected from back grinding, polishing,and etching (these are referred to as “back grinding or the like”) toproduce a substrate with a thickness in the range of 50 μm to 200 μm,say 100 μm. Although etching is not strictly grinding, the means todecrease a thickness of the substrate is not limited in thisspecification and etching is also regarded as a means of grinding.

Then, as shown in FIG. 6, phosphorus, n type ions, and boron, p typeions, are implanted from the rear surface of the substrate followed byheat treatment (e.g. annealing) in an electric furnace at a temperaturebetween 350° C. and 450° C., to form a buffer layer 10 and a collectorlayer 8 in the rear surface region of the substrate. After that, asshown in FIG. 7, an aluminum-silicon film, a conductive film, is formedby evaporation or sputtering as a first layer of a multilayeredcollector electrode (rear electrode) 9 on the collector layer 8, thatis, on a rear surface of the substrate.

The aluminum-silicon film is formed so that the silicon concentration isin the range of 0.5 percent to 2 percent by weight, preferably not morethan 1 percent by weight, and the thickness is at least 0.3 μm. Athickness of the aluminum-silicon film more than 1.0 μm would beunfavorable, because warping in the substrate would then becomesignificant, increasing assembly defects. Forming an aluminum-siliconfilm under the conditions specified above prevents the generation ofaluminum spikes. Consequently, the proportion of defective devices isreduced.

Subsequently to the aluminum-silicon film, a plurality of metal films oftitanium, nickel, and gold are deposited by evaporation or sputtering toform a complete collector electrode 9. The titanium film, the nickelfilm, and the gold film are employed as a buffer metal film, a solderingmetal film, and a protective metal film, respectively, and it will beappreciated by those skilled in the art that other metals may beemployed without departing from the scope of the invention. The buffermetal film can also be formed of molybdenum, for example.

Finally, as shown in FIG. 8, a dicing tape 13 is stuck on the side ofthe collector electrode 9, to divide into plural chips 14. Each chip 14is mounted in various apparatuses, in which the collector electrode 9 issoldered to an anchoring member of the apparatus and the surfaceelectrodes including the emitter electrodes of the chip are affixed withaluminum wiring electrodes to the apparatus by an ultrasonic wirebonding device.

FIG. 9 is an electron micrograph showing a surface condition of asilicon surface that was prepared by the following process. Analuminum-silicon film was formed by evaporation or sputtering under theabove-described conditions of thickness and silicon concentration, andthen, the aluminum-silicon film was removed using aqua regia to expose asilicon surface. FIG. 10 is an electron micrograph of a surfacecondition that was prepared by first forming an aluminum film in placeof aluminum-silicon film and then removing the aluminum film by aquaregia to expose a silicon surface. Flaws generated by aluminum-spikescan be observed in FIG. 10, but no flaw can be seen in FIG. 9. Thisillustrates that the first embodiment prevents the generation ofaluminum spikes.

When the first layer of the collector electrode in contact with thecollector layer 8 is an aluminum film having a thickness not less than0.3 μm, generation of aluminum spikes is reduced. When the first layeris an aluminum alloy film (silicon concentration thereof is notspecified) having a thickness not less than 0.3 μm, the generation ofaluminum spikes is avoided or at least reduced. When the first layer ofthe collector electrode 9 is an aluminum alloy film having a thicknesssmaller than 0.3 μm for example a thickness of about 0.1 μm, thealuminum alloy film preferably contains silicon in a concentration of atleast 2 percent by weight. This condition can also prevent generation ofaluminum spikes. These points will be described in detail below, inreference to the second embodiment.

Second Embodiment

FIGS. 11 through 14 are sectional views illustrating a method ofmanufacturing a reverse blocking IGBT according to the presentinvention. Referring to FIG. 11, a p type isolation region 15 is firstformed in an n− FZ substrate that works as an active layer (a driftlayer) 1 by selective thermal diffusion of p type ions from above. Toproduce a device of a rating voltage of 1,200 V, the p type ions arediffused to a depth of about 200 μm.

Subsequently, as shown in FIG. 12, a front surface side device structureis formed in the surface region of the FZ substrate surrounded by theisolation region 15, the device structure being composed of a baseregion 2, an emitter region 3, a gate oxide film 4, a gate electrode 5,an interlayer insulation film 7, and emitter electrode 6, and aninsulation protective film (not shown in the figure). Then, the rearsurface of the substrate is ground by back grinding or the like, untilthe isolation region 15 is exposed as indicated by a dotted line in FIG.12.

Then, as shown in FIG. 13, p type ions are implanted from the rearsurface of the substrate, followed by heat treatment (annealing), toform a collector layer 8 in the rear surface region of the substrate.After that, on the surface of the collector layer 8, aluminum film 16 isdeposited by evaporation or sputtering as a conductive film of a firstlayer of a multilayer collector electrode (a rear electrode) 9. When thethickness of the aluminum film 16 is at least 0.3 μm, for example 0.6μm, generation of aluminum spikes is reduced. Therefore, the proportionof defective devices is reduced.

Subsequently to forming the aluminum film 16, as shown in FIG. 14, ametal film 17 including a plurality of metallic films of titanium,nickel, gold, or the like is formed by evaporation or sputtering to forma complete collector electrode 9. Finally, dicing is conducted to dividethe substrate into a plurality of chips, similarly to the firstembodiment.

The same effect can be obtained when the first layer of the collectorelectrode 9 that is in contact with the collector layer 8 is composed ofan aluminum alloy film (irrespective of silicon concentration) having athickness of at least 0.3 μm. When the aluminum alloy film is thinnerthan 0.3 μm, for example 0.1 μm, the aluminum alloy film preferablycontains silicon in an amount of at least 2 percent by weight. Thismeasure prevents the generation of aluminum spikes as well.

FIGS. 15 through 17 are electron micrographs showing the surfaceconditions of the samples that were prepared by forming a multilayeredelectrode, the first layer of which is an aluminum film, on a siliconsurface by means of evaporation or sputtering, followed by heattreatment, and then removing the electrode using aqua regia to exposethe silicon surface. FIG. 15 is a photo of the sample with an aluminumfilm thickness of 0.1 μm. Flaws about 0.2 μm deep are observed that weregenerated by aluminum spikes on the silicon surface.

FIG. 16 and FIG. 17 are photos of the samples with aluminum filmthicknesses of 0.4 μm and 0.6 μm, respectively. Cross-sections of thesesamples were observed by the electron microscope and are shown in FIG.18 and FIG. 19. FIGS. 16 through 19 indicate that the flaws due toaluminum spikes were smaller. A sample with an aluminum film thicknessof 0.3 μm also showed relatively small flaws.

Thus, the second embodiment prevents generation of aluminum spikes whenthe first layer of a multilayer electrode is composed of an aluminumfilm having a thickness of at least 0.3 μm. FIG. 20 shows depth of flawsdue to aluminum spikes and the proportion of non-defective devices independence on aluminum film thickness. As shown in FIG. 20, when thealuminum film thickness is at least 0.3 μm, the flaws due to aluminumspikes are shallower than the thickness of the collector layer 8, forexample, and the proportion of non-defective devices is improved.

FIGS. 21 through 23 are electron micrographs showing surface conditionsof the samples prepared by forming a multilayer electrode, the firstlayer of which is an aluminum-silicon film, on a silicon surface bysputtering, followed by heat treatment, and removing the electrode usingaqua regia to expose the silicon surface. FIG. 21 is a photo of a samplewith an aluminum-silicon film thickness of 0.1 μm. Flaws generated onthe silicon surface by aluminum spikes can be observed.

FIG. 22 and FIG. 23 are photos of the samples having aluminum-siliconfilms with thicknesses of 0.4 μm and 0.6 μm, respectively. No flaw dueto aluminum spikes is observed in either of these photos. A similarresult has been obtained in a sample with a thickness of analuminum-silicon film of 0.3 μm. A thickness of aluminum-silicon film of0.4 μm or more in particular, never generates any flaw due to aluminumspikes. Although some pieces called silicon modules still exist, theyhave no unfavorable effect on the proportion of non-defective devices.

According to the second embodiment, generation of aluminum spikes isprevented with a first layer of a multilayer electrode composed ofaluminum-silicon film having a thickness of at least 0.3 μm. FIG. 24shows a result of a study on the relation between the thickness of thealuminum-silicon film and the proportion of non-defective devices. It isapparent from FIG. 24 that a thickness of the aluminum-silicon film of0.3 μm or more results in an improvement in the proportion ofnon-defective devices.

FIG. 25 shows a result of a study on the relationship between thesilicon concentration and the proportion of non-defective devices forvarious silicon concentrations in aluminum-silicon films prepared bychanging target materials in the sputtering apparatus, with a fixedthickness of the aluminum-silicon film of 0.1 μm. It is apparent fromFIG. 25 that a silicon concentration of the aluminum-silicon film of 2percent by weight or more improves the proportion of non-defectivedevices. Thus, when the first layer of the multilayer electrode iscomposed of an aluminum-silicon film having a relatively smallthickness, for example thinner than 0.3 μm, the second embodiment alsoprevents generation of aluminum spikes by setting the siliconconcentration at least 2 percent by weight.

The present invention shall not be limited to the embodiments describedabove, but any variation and modification is possible within the spiritand scope of the invention. For example, in the above embodiments, thefirst conductivity type is n type and the second conductivity type is ptype. However, the invention is also effective when the firstconductivity type is p type and the second conductivity type is n type.

As described above, the method of producing a semiconductor deviceaccording to the invention is useful for producing a semiconductordevice with a thin device thickness. This method is particularlysuitable for producing power semiconductor devices including IGBTs thatare applied to industrial apparatus such as general purpose invertors,ac servo systems, uninterruptible power supplies (UPSs), and switchingpower supplies, and consumer appliances such as microwave ovens,electric rice cookers, and electric flash lights.

1. A method of producing a semiconductor device that has a front surface device structure in a region of a first major surface of a silicon substrate and a rear electrode in a region of a second major surface of the silicon substrate, the method comprising the step of: forming an aluminum-silicon film in contact with the second major surface as the rear electrode, wherein the semiconductor device is a reverse blocking type insulated gate bipolar transistor that includes, between the first major surface and the second major surface, a drift layer of a first conductivity type, and a collector layer of a second conductivity type provided in sequence from the first major surface, the drift layer being surrounded by a semiconductor layer of the second conductivity type including the collector layer, wherein the rear electrode is in contact with the collector layer, and wherein the aluminum-silicon film comprises an aluminum alloy with a silicon concentration of at least 2 percent by weight.
 2. A method of producing a semiconductor device that is a reverse blocking type insulated gate bipolar transistor that includes: (a) a silicon substrate with a first major surface and a second major surface, and provided in sequence from the first major surface to the second major surface, a drift layer of a first conductivity type, and a collector layer of a second conductivity type, the drift layer being surrounded by a semiconductor layer of the second conductivity type including the collector layer; and (b) a rear electrode in contact with the collector layer, the method comprising the step of: forming, as the rear electrode, a film of aluminum or an aluminum alloy having a thickness of at least 0.3 μm in contact with the collector layer.
 3. A method for producing a semiconductor device having a silicon substrate, the silicon substrate having a first major surface for forming a front surface device structure thereon, and a second major surface for forming a rear electrode thereon, comprising: forming a drift layer and a collector layer in the substrate in sequence from the first major surface, the drift layer being of a first conductivity type, and being surrounded by a semiconductor layer of a second conductivity type including the collector layer; and forming an aluminum silicon film on the second major surface for the rear electrode.
 4. The method of producing a semiconductor device according to claim 3, further comprising forming a buffer metal film on a surface of the aluminum-silicon film.
 5. The method of producing a semiconductor device according to claim 4, further comprising: forming a soldering metal film on a surface of the buffer metal film; and forming a protective metal film on a surface of the soldering metal film.
 6. The method of producing a semiconductor device according to claim 4, wherein the buffer metal film comprises one of titanium or molybdenum.
 7. The method of producing a semiconductor device according to claim 3, wherein the aluminum-silicon film has a thickness of at least 0.3 μm, and is an aluminum alloy having a silicon concentration of at most 1 percent by weight.
 8. The method of producing a semiconductor device according to claim 3, wherein the aluminum-silicon film has a thickness of at least 0.3 μm and at most 1.0 μm, and has a silicon concentration of at least 0.5 percent and at most 2 percent by weight.
 9. The method of producing a semiconductor device according to claim 3, further comprising making the silicon substrate to have a thickness in a range of 50 μm to 200 μm, before the step of forming the aluminum-silicon film.
 10. The method of producing a semiconductor device according to claim 3, wherein the method produces a field stop type insulated gate bipolar transistor that comprises, between the first major surface and the second major surface of the silicon substrate: the drift layer of the first conductivity type, a buffer layer of the first conductivity type, and the collector layer of the second conductivity type in a sequence from the first major surface, and has a structure having the collector layer in contact with the aluminum-silicon film.
 11. The method of producing a semiconductor device according to claim 10, wherein the aluminum-silicon film has a thickness of at least 0.3 μm and at most 1.0 μm.
 12. The method of producing a semiconductor device according to claim 11, further comprising making the silicon substrate to have a thickness ranging from 50 μm to 200 μm before the step of forming the aluminum-silicon film.
 13. The method of producing a semiconductor device according to claim 11, further comprising the step of making the silicon substrate to have a thickness ranging from 50 μm to 200 μm before the step of forming the aluminum-silicon film.
 14. The method of producing a semiconductor device according to claim 10, further comprising the step of making the silicon substrate to have a thickness ranging from 50 μm to 200 μm before the step of forming the aluminum-silicon film.
 15. The method of producing a semiconductor device according to claim 3, wherein the semiconductor device is a field stop type insulated gate bipolar transistor that includes, between the first major surface and the second major surface: the drift layer of the first conductivity type, a buffer layer of the first conductivity type, and the collector layer of the second conductivity type in a sequence from the first major surface, wherein the rear electrode is in contact with the collector layer. 